1. Field of the Invention
The present invention relates to a starch replacement composition which is used to prepare starch-based corrugating adhesive compositions and the adhesive compositions prepared therewith. In particular, the invention has to do with a dry blend pre-mixture composition comprising starch and ground plant germ. The pre-mixture is employed as a complete or partial replacement for starch in a carrier, no-carrier or carrier-no-carrier corrugating adhesive.
2. The Related Art
In the corrugating process, adhesive is commonly applied to the tips of the flutes of a corrugated medium. Then a noncorrugated flat paper liner is applied against the adhesive coated flutes as they pass between a corrugating roll and a pressure roll. The resulting product has the corrugating medium on one side and a flat liner on the other side and is called a single-face portion. The single-face portion may be used "as is" (called a "single face" board) or adhesive may be applied to the flute tips of the single-face portion and a second flat sheet can be applied in the same manner as the first in what is called a "double-face" or a "double-back" operation. The second liner sheet is treated with heat and reduced pressure (relative to the pressure used to make a single-face portion) immediately following contact with the adhesive.
Starch-based adhesives which can be of the carrier, no-carrier and carrier-no-carrier type are commonly used in processes for manufacturing corrugated paper board. In carrier type adhesives, a portion of the starch (or dextrin) forms a carrier, often known as the gelatinized phase, which suspends the balance of the starch which is in an ungelatinized state. Under conditions of heat and pressure, the ungelatinized starch is rapidly hydrated and gelatinized to increase quickly the viscosity and adhesivity of the adhesive composition. In no-carrier type adhesives, all of the starch is slightly cooked or swollen with heat and caustic soda for viscosity. Finally, carrier-no-carrier type adhesives have a portion of the starch which forms a carrier and is responsible for about one half of the viscosity and the remaining viscosity is obtained by slightly swelling the uncooked starch.
Corrugating adhesives having a solubilized cellulosic fiber component are described by Fitt in U.S. Pat. No. 5,358,559 and by Giesfeldt et al. in U.S. Pat. No. 5,503,668. These adhesives are prepared employing in situ solubilization processes which are carried out in the primary mixer when preparing a two-part Stein-Hall carrier paste. This is contrasted with the present invention wherein ground plant germ is added to the primary and secondary mixers and wherein the processing conditions in the secondary mixer are not designed to cause in situ solubilization.
According to U.S. Pat. No. 4,941,922, long thin fibers can be added to starch-based corrugating adhesives to enhance adhesion based on a mechanism of fiber-to-fiber entanglements. These entangling fibers are said to enhance dispersion and yield improved adhesive characteristics including increased waterproofness, dry strength, viscosity and adhesiveness. Suitable sources of fiber are described as cellulosic fiber including wood, paper, cotton and rayon; fibers of synthetic origin including Nylon, polyester, polypropylene, Lycra Spandex, Vyrene, Vinyon, Dynel, Saran, Creslan, Acrylic, polyethylene, Teflon, tetrafluoroethylene, glass, Corlon and metallic fibers. Fibers generated during the wheat or corn milling processes are also said to be suitable. According to the patent, the fibers typically are suspended initially in the uncooked starch portion, suspended with the carrier portion, suspended prior to the carrier-no-carrier (or no-carrier) swell or added to the final adhesive mixture prior to storage or use. There is no experimental data in the patent, however, describing the use of fibers generated during the corn or wheat milling processes. Furthermore, the fibers must be present in an amount from about 2.2 to about 22 pounds of fiber per 100 pounds of corrugating adhesive and must have a diameter of between about 0.0005 inches and about 0.02 inches and a length of between about 0.025 inches and about 0.25 inches to cause fiber-to-fiber entanglements. In contrast, the ground plant germ of the present invention is not long and thin, the shape more closely approximates spheres or cubes, and the germ is believed to enhance adhesive properties because it is sticky.
The present invention also has the surprising advantage that a commercially viable adhesive paste can be made with no boron compound or a substantially reduced amount of boron compound.
In the present specification and claims, all parts and percentages are by weight/weight (w/w) unless otherwise specified, and the term "parts of adhesive" is used to refer to the total weight of adhesive, including water, starch, plant germ and all chemicals. The term "parts of carrier phase" is used to refer to the total weight of the carrier phase, including water, starch, plant germ and all chemicals. The term "total solids" is used to refer to the total dry basis ("d.b.") weight of the ingredients of the adhesive or the carrier phase or suspended phase thereof, including starch and plant germ but not including chemicals such as caustic, borax and the like.